<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>

        window.onload = function () {
            let aList = ['a', 'b', 'c'];
            aList.map(function (item, i) {
                alert(item);
                alert(i);
            })

            let onw = aList.concat(['d', 'r', 'g']);
            alert(onw);
        }


    </script>

</head>
<body>

</body>
</html>